The principal objectives of this project are the continuing efforts to identify antiplaque and anticaries agents suitable for short-term clinical investigation, as well as to develop methods for assessing the clinical potential for these agents. The present study investigated a method of estimating the resistance of tooth enamel to an acid challenge when used in vitro or in vivo. This method, termed the acid neutralization time or ANT, measures the time required for the tooth to neutralize two microliters of acid contained in a paper disc impregnated with a pH Indicator. Findings from in vitro tests indicate that the method is simple, relatively reproducible and can detect the effects of fluoride treatments on enamel solubility.